1. Field of the Invention
The present invention relates to header pipes for a heat exchanger with tubes connected thereto for heat exchange through a medium and designed to distribute and collect the medium.
2. Description of the Related Art
In general, any conventionally known heat exchanger comprises a plurality of tubes laminated with fins interposed and header pipes disposed at opposite ends of tubes, the header pipes respectively having tube insertion holes into which opposite ends of each tube are inserted respectively to be connected with the header pipes, an inlet joint and an outlet joint respectively connected to a header pipe so that heat exchange can be effected while the heat exchange medium flows by meandering a plurality of times through the tubes disposed between the inlet joint and the outlet joint of the header pipes.
In the header pipe used in this type of heat exchanger, a plurality of tube insertion holes are longitudinally formed by being pitched at predetermined intervals, and the inside of each header pipe is divided by partitions provided at predetermined positions, whereby heat exchange medium is distributed and collected for circulation by units of tube groups.
Such a header pipe is provided with an extended portion longitudinally extending from the portion where tube insertion holes are formed. The extended portion serves for providing the inlet joint and the output joint and also for supporting a bracket for installation of heat exchanger.
However, as shown in FIG. 7, for example, in the case of a conventional heat exchanger 20, for the purpose of using a common mold, common header pipes 21 (only one of them is shown) are used for both the left and right header pipes. As a result, in the header pipe not provided with neither the output joint nor the inlet joint, an extended portion 21a extending outside of a side plate 8 which is not provided with either the output joint or the inlet joint.
Such an extended portion as the extended portion 21a of the header pipe 21 is much inferior in strength to the portion provided with tube insertion holes 9, 9 and, of such header pipes, those obtained by forming the flat-sheet material into pipes are particularly apt to be deformed or ruptured.
This results from (1) that while the portion having the tube insertion holes is reinforced by being connected to the tubes, the extended portion without the tube insertion holes is not reinforced by the tubes. That is, the end of each tube inserted into the tube insertion hole acts as a reinforcement to resist deformation or internal pressure, so that the portion provided with the tube insertion holes is reinforced by the units of the intervals of the tube insertion holes. On the other hand, such an extended portion, lacking in the reinforcement by being connected to the tubes, is weaker in relative strength.
Further, (2) the peripheral region of each tube insertion hole is formed with a projecting edge (hereinafter referred to as a burring) for the purpose of increasing a brazing area with the end of tube. The portion formed with the tube insertion holes are reinforced with the burring and brazing material deposited on the burring. For this reason, therefore, the header pipe material having a thickness of more than necessary has to be used merely for increasing the strength of such extended portion.
Furthermore, (3) in forming the header pipe by shaping the header pipe material with the tube insertion holes and burrings, the recoiling force (hereinafter referred to as spring back) of the header pipe material can be suppressed to a certain extent due to the existence of the burrings. As a result, there occurs some differences in the spring back between the portion provided with the tube insertion holes and the extended portion without the tube insertion holes, causing an inconvenience such that the opposite ends of the portion provided with the tube insertion holes can be fit snugly along the seam, while the opposite edges of the extended portion are apt to separate along the seam to a degree that the joining along the seam become impossible, or the cap cannot be fitted.
In order to avoid such inconvenience, the material having a thickness large enough to increase the strength of the extended portion has to be used despite that the portion of the header pipe provided with the tube insertion holes need not be formed by using the material of such thickness, causing, as a result, the whole header pipe should be formed using the material having a thickness and rigidity more than necessary.